Automatic flight control systems for aircraft



April 13, 1965 K. FEARNSIDE ETAL AUTOMATIC FLIGHT CONTROL SYSTEMS FOR AIRCRAFT Filed July 19, 1962 y. /A/vEn/TORS KEMA/Em FEAENS/DE HEM/z PQLLAK 5) @frag/4%? /ZD United States Patent O 3,178,134!- AUI'MATC FLIGHT CNTRL SYS'EMS FR ARCRAFT Kenneth Fearnside, Bredon, near Tewkesbury, and Heinz Pollalr, Bishops Cleeve, Cheltenham, England, assignors to S. Smith @t Sons (England) Limited, London, England, a British company Filed July i9, 1962, Ser. No. 210,97 16 Claims. (Cl. 24d-77) The present invention relates to automatic flight control systems for aircraft and is concerned in particular with systems which are capable of controlling an laircraft automatically during the whole of a landing manoeuvre.

It has 'been proposed to provide an automatic control system for this purpose which operates in such a manner that the landing manoeuvre is divided into various phases, as follows, the heights specified 'being by way of example only and being, of course, variable within limits according to requirements.

(i) Manoeuvring to fly on to a glidepath as defined by the localiser and glidepath beams of a conventional I.L.S. system; the track phase.

(ii) Flying down the glidepath, maintaining constant air speed and pitch attitude; the glide phase.

(iii) From a height of say l() ft., the glidepath signals of the I.L.S. system being no longer usable, continuing to fly down an extension of the glidepath, maintaining the same airspeed and the mean pitch attitude subsisting during the last part of the glide phase; the attitude phase.

(iv) From a height of say 50 ft` commencing the flare that is to say starrting to following a path which, in the vertical plane, is curved so as to level out smoothly to the surface of the runway and at the same time closing the throttles; the liare phase.

(v) -From a height of say 3() ft., continuing the flare, and, if there is any drift due to a cross wind component, controlling the rudder and ailerons at some preselected altitude so as to rotate the aircraft in yaw, maintaining the wings level, to align its fore and aft axis with the runway; the land phase.

In phases (iii) to (v), azimuth guidance may still be obtained, up until the moment of kicking-olf drift, from the localiser Ibeam of the ILS. system, if suitable, or from a leader cable guidance system such as that described in British Patent Specification No. 820,319.

Of these phases, phases (i) and (ii) are conventional landing approach practice during which an automatic pilot included in the control system is set by means of switches or `other controls to operate in known manner under the control of signals supplied to it, inter alia, from glidepath and localiser receivers provided in the aircraft to manoeuvre the aircraft until it is positioned on the glidepath and then to maintain it on the glidepath whilst flying down it (conventional automatic night control systems for aircraft often include facilities for coupling an automatic pilot to suitable signal sources in the manner required to 'brinr this about, the intention being with a conventional system, that the automatic control can be used to control the aircraft down to an altitude of say 200 ft. after which a human pilot must take over control). In addition, the airspeed may be maintained at the required value either manually or preferably by an automatic throttle control system forming a part of the ight control system as a. whole.

In phase (iii), it has been proposed that the control system should operate to maintain the mean pitch attitude subsisting during the last part of phase (ii), azimuth guidance being obtained from signals derived either from a localiserl receiver or `from a leader cable signal receiver. The signals from a localiser receiver may be employed provided that the 4transn'iitter is situated along the centre line of the runway concerned and in addition that the localiser system as a whole is of sufficient inherent accuracy. The aircraft is also maintained level in rbanlt apart from any correcting manoeuvres required to maintain the aircraft on the correct heading on the glidepa-th. The airspeed is maintained at the same value as in phase (ii).

ln phase (iv), it has been proposed that the elevator channel of the automatic pilot should commence to operate in response to signals from a frequency modulated radio altimeter to control the elevators in such a manner that the aircraft (considering only vertical manoeuvres) is manoeuvred to fly as closely as possible to a datum flare path defined by an equation such as;

where 1 is a time constant of magnitude, say 4-8 seconds, D is the diilcrential operator d/dt (t representing time) and h is the aircrafts altitude relative to a datum which may be ground level or a level a few feet above or below ground level. At the commencement of phase (iv), the throttles are closed either manually or automatically if automatic throttle control is provided.

Further according to these proposals, in phase (v), the elevator control continues as in phase (iv) but any drift angle is removed, shortly before touching down, by an operation equivalent to that known by human pilots as kicking-'olf drift, the rudder being operated under automatic control to rotate the aircraft about its yaw axis until its fore and aft axis is aligned with the runway and the ailerons being operated simultaneously to prevent any roll.

During the land phase, the wings of the aircraft must be held substantially level to obviate any possibility of a wing tip touching the ground. However, if there is any cross wind component, it will be necessary, as envisaged above to carry out automatically an operation equivalent to kickingolf drif Since, when this operation requires to be carried out, the aircraft can not be steered by banking, it has been proposed to operate the rudder, at a suitable moment as determined by radio altimeter signals and under thepcontrol of switches operated under the control thereof, in dependence upon a signal representing the difference between the aircrafts heading and the direction of the runway and in particular to apply the rudder at a rate proportional to this heading error signal in a sense such as to yaw the aircraft on to the desired heading.

When this is done, a rolling moment will be applied to the aircraft, owing to the inherent coupling of its yawing and rolling motions, tending to dip the wing on the inside of the turning movement. The ailerons must therefore be operated simultaneously to oppose this moment and to maintain the wings substantially level. Rolling moments tending to disturb the aircrafts bank attitude will occur also at other times during the flare and land phases, for example on operation of the rudder to prevent yawing and also if there is any change in the lateral Wind or i-n the rate of yaw of the aircraft. When drift is kickedolf there will be an effective change in the lateral wind and it may also change at any time due to natural causes e.g. due to gusting. It is therefore necessary to feed the aileron channel of the autopilot with signals which will enable it to counter any of these rolling moments at the earliest possible moment and thus to minimise or even eliminate their effects.

The present invention is concerned particularly with the control of an aircraft automatically during the operation of kicking-off drift and also during the flare phase of a landing` It will be appreciated that whilst the invention is applicable and indeed has been developed in connecit tion with automatic Hight control Systems of the kind capable of controlling an aircraft whilst carrying out a landing in the manner described above, it is in fact applicableto any other systems 4for the same purpose, pro# videdthat ilare and land phases (or their equivalents) Y similary to those set out above are included.

or both of the said phases and at least from the momentl of initiating the operation of kicking-off drift, `a component signal which is derivedA from the accelerometer and represents a function of the aircrafts lateral acceleration the'signal being applied in a sense such as to oppose any tendency of the aircraft tobank. v

By demand signal is here meant a signal which is applied to a servo system for controlling the operation of the ailerons or other control surfaces and represents, in `a manner whichwill depend in part on the particular characteristics of the servo system and in part on the purpose for which the demand signal is applied, a demand to the servo system` for movement or positioning'of the aileron or other control surfaces. Thus, for example, if the servo system is a conventional position servo, the 'demand signal may represent a demanded aileron position, and will usually include a basic control term representing or dependent on the Vairorafts actual bank attitude, as measured for example by a vertical gyroscope. In a simple rateservo, the demand signal may similarly represent a demanded rate of aileron movement and will usually include a basic control term representing'or dependent on the aircrafts rate of bank, as measured for example by one or more rate gyroscopes. Said component signal would in all cases be applied in a sense to counteract any rolling'movement arising, for example' The demand signal may further include derivatives of any or all ofthe further components and the one component may represent a function of the lateral acceleration which is or includes one or more derivatives thereof.

The lateral accelerometer may be a lateral-pendulum,

that is to say a pendulum mountedin the aircraft for free rotationabout an axis parallel to the fore and aft axis of the aircraft, the pendulum preferably being lmounted at a point forward of the aircrafts centre-of-gravity, anda signal representing `any angular deflection of the moving parts of the pendulum from `their datum position (i.e. vertical whenthe aircraft is still and level) may then be employed as a signal representing the aircrafts'lateral acceleration. The accelerometer is required to measure side-slipfbut, i-n fact, will detect any side-force acting on the aircraft. If it is ysuitably positioned forward of the centre of gravity of the aircraft, most of the force measured will be due to side-slip, at least during the manoeuvre under consideration, but there may still bea component due to operation of the'rudder. Any'siich component may be compensated by a further component, the fourth listed above, arising fromr movement of the rudder. If the accelerometer is near the centre of gravity, the effect of the rudder willbe greater.

At the Same time, a system according to the present invention may include means for controlling the aircrafts rudder or equivalent control surfaces in accordance with a demand signal having a irst component which is a function of any difference between the aircrafts heading and a set direction which is set in operation to` be that'of the runway in the direction of landing, and, if required, further components which may include:

(i) -aV component representing a function of aileron position, and

(ii) one or more components representing functionsl of the aircrafts rate of yaw and the rate of change thereof.

The relevant parts of an example of an automatic iiight control systemaccording to the present invention will now be described by way of examplewith' reference to the accompanying drawing in which:

FIGURE l shows a block circuit diagram-of the parts of the system. K

The flight' control system of which a blockdiagram of parts of the rudder and aileron channels is shown in FIGURE l, is one which is built around an automatic pilot employing the rate/rate system of control, i.e. one

in which the control surfaces are moved by 'servo systemsY at a rate determined by demanded rate of movement signals applied y to the inputs,V of the servo systems.

which apply from the moment of initiating theautomatic kicking-cfrFV drift operation and it will be understood that switches (not shown) are provided to change the interconnections where necessary and to introduce further connections to additional signal sources for other modes of operation of the system.

FIGURE 1 shows a servo amplifier 1V provided for 'the' aileron control channel, the output of the amplifier ll controlling the energisation of the control phase winding 2a of a, two phase induction servo motor 2.l The servo motor 2 has a reference phase winding 2b which is connected to terminals across which a reference voltage source 3 (not shown) is connected in operation. The motor 2 drives arshaft 4 by which is driven a tachometer generator 5 for generating a feedback signal representing the rate of rotation of the shaft 4 and the input member of an electromagnetic clutch 6.` The input winding of the tachorneter generator 5 is connected across terminals 7 to which, like terminals 3, a suitable reference voltage source is coupled in operation. The output Winding of the generator 5 is coupled to an input of the amplifier-1, providing a rate feedback voltage in known manner. The' coil of the clutch 6 is connected in a conventional D.C. energising circuit (not shown) which includes switches for determining whether or not the circuit is completed and thus whether the output drive from the aileron channel of the automatic pilot is engaged or not.

The output member of the clutch 6 is mounted on a further shaft'S whichis coupled to whatever form of aileron actuator 9 is provided in the aircraft concerned, The output of the actuator is shown coupled directly by shafts 19 to a pair of aileron surfaces 11. It will be appreciated that the arrangement of shaft 8,'actuatoi* Si and shaftsltl shown coupling'the output member of the clutch 6 to the yailerons l1' is in fact simplified and that it may take many forms depending on the form of actuator and control run provided in a particular aircraft. For example, the shaft S may drive part of the control run directly, the latter then Vproviding an input drive to Y some form of hydraulic actuator of which there may be As shown in FGURE l, the inter-connections are thosev will be described further in connection with the rudder channel.

Apart from the two feedback signal inputs already described the amplifier 1 has a third input which is coupled to the output of a signal summing network 1S having four separate inputs, the output of the network in operation being a signal representing a demanded rate of aileron movement. For the particular aircraft for which the system was designed a demanded rate of aileron move ment signal (DSD given by the following equation was found suitable.

where n1, F1, F2, F3 and F4 are constants, T1 is a constant having the dimensions of time, D is the differential operator d/dt, ,S is aileron position, (De) is the aircrafts actual rate of bank relative to a set of gravity axes, [31, is the deviation angle of a lateral pendlum, y is the aircrafts rudder position and r is the aircrafts rate of turn about its yaw axis.

The first term on the right hand side of Equation 1 is employed in all modes of operation of the system, being a signal representing the aircrafts rate of bank with some phase advance as determined by the values of nl, and T1, in known manner, and from which according to the different modes of operation is subtracted a signal representing a demanded rate of bank (DMD with or Without other terms for balancing and datum adjusting purposes. A signal representing this term is supplied to one input of the summing network 15 from the output of a shaping network 16 having phase advance characteristics such that its output represents the input when operated by the operational function (l-{-n111D)/ (i+1-1D). This network 16 may be of any known and suitable form.

The input to network 16 is a signal representing (De) which is generated to a degree of approximation by surnming, in network 17, signals representing the quantities p (the aircrafts rate of turn about its roll axis) and r6, where r is the aircrafts rate of turn about its yaw axis and is its pitch attitude. The expression (p4-r6) is taken as an approximation to the expression which properly represents the quantity (De) in terms of p and r for a given pitch angle 6*. Signals representing p and r are generated by pick-offs associated with suitably oriented rate gyroscopes 18 and 19 forming part of the basic automatic pilot and mounted on a platform fixed in the aircraft. The gyroscopes 13 and 19, together with a third gyroscope 2t) for providing a signal representing the aircrafts rate of turn q about its pitch axis, are included in a rate gyroscope unit 21. The output of gyroscope 2li is utilised, in known manner and as indicated in FIGURE l, in the elevator channel of the automatic pilot.

The basic automatic pilot further includes a vertical gyroscope 22 having output shafts 23 and 24 which are positioned in accordance with the aircrafts pitch and bank angles 6 and fp. Both shafts drive pick-offs 2S or 26 e.g. synchros and/or potentiometers of which more than one may be provided on both shafts although only one is shown in each case. The signals from these pickoffs and 26 are utilised respectively in the elevator channel of the automatic pilot and in the aileron channel in modes other than that presently considered. The shaft 23 further drives the shaft of a potentiometer 27 across the whole resistance of which is applied a signal representing r from gyroscope 19. The voltage across the slide and one end of the resistance will then represent r@ and this voltage is applied to one input of summing network 1'7, the other input of which is supplied with a signal representing p from gyroscope 13. The output from network 17 thus represents as required the quantity (p-l-r) or (De).

A second input of network 15 is coupled to the output of shaping network 2S which in this case is a differentiating network and is supplied with a signal representing r from rate gyroscope 19. The output of network 23 then represents the quantity Dr, as required to provide the fourth term on the right hand side of Equation l. T his term is included in the sense to counteract any rolling movement arising from yawing motion.

A third input to network 15 is derived from a lateral pendulum unit Z9, that is to say, a unit including a pendulum mounted for free angular displacement about an axis parallel to the fore-aft axis of Ithe aircraft, the

pendulum being mounted preferably forward of the` centre of gravity of the aircraft. The third input to the network 15' is derived from the unit 29 through a shaping network Sti which again in this case is a differentiating network giving lan output Dp where [3p is the angular deflection of the pendulum from its datum position (i.e. vertical when the aircraft is still and level) as this is represented by lan output signal obtained from a pick-off associated with the pendulum. This provides a signal representing the second term on the right hand side of Equation l.

The remaining input to network 1S comes from a network 31 which, as described below in connection with the rudder channel, receives at its input a signal representing the rudder position g. Network 31 is again a differentiating network and provides an output representing D5" as required to provide the third term on the right hand side of Equation l. This component, again is included in the sense required to counteract any rolling moment arising from opeuation of the rudder and also to compensate, if necessary, for any effect which operation of the rudder rnay have on the lateral pendulum.

The summing network 15 operates to combine the signals from networks 16, 28, 3ft and 31 in the proportions and in the senses required by the constants and signs in Equation l, the constants lil-F4L being determined, it will be appreciated, in accordance with the aircrafts characteristics.

The rudder channel is similar to the aileron channel having a servo amplifier 35 controlling a servo motor 36, the shaft 37 of which drives a tachometer generator 3S and the input member of ian electromagnetic clutch 39. The output of .the tachometer generator is fed back to an input of the amplier 35 to provide rate feedback, whilst the output member of the clutch 39 drives a shaft 46 and through it a rudder actuator 41, shaft 42 and the rudder 43, this latter combination being, as with the ailerons a simplified schematic one shown for the purposes of description only. The shaft 4Z drives a rudder position pick-off 32 the output of which is fed to the input of network 31 in the aileron channel in accordance With the requirements previously described above.

The remaining input of the servo amplifier 3S is supplied in operation with a signal representing a demanded rate of rudder movement (D )D given by the equation:

(2) where H1, H2, H3, a, and .n3 are constants, E, D and r are as previously defined, f2 and f3 are constants with the dimensions of time, rb is the aircrafts heading and gbr is a set heading representing the direction of the runway centre line in the direction chosen for landing. The signal representing (DDD is generated in a summing network 44, the output of which is fed to the demand signal input of amplifier 35. Network dit has three inputs, the connections to which are described below.

A signal representing the first two terms on the right hand side of Equation 2 is supplied to one input of summing network 44 from a shaping network 45 which is fed with a signal representing r from the rate gyroscope 19. Network 45 has two parallel channels one a simple proportional channel and the other having a transfer iva/(Hao).

(1+n3f3D)/(1+T3D) The input/of network 46 is coupled tothe output from the motor of`a synchro'tr'ansfo'rmer 47, the stator of which is energised in accordance with aircrafts heading `1// by si'gnals'from 'a conventional gym-magnetic compass system 48. Ashaft 49 is adjusted manuallyby means of aV knob Sil to position therotor of the synchro 47 in accordance with the direction of the runway on which it is desired to land, this adiustrnentbeing made previously to the commencement of that phase of the landing which is being considered here and probably before the landing manoeuvre' is commenced.' The signal from the motor of synchro 47 thus 'represents (gb-dr) land the output from network 46 thus takes the form required to provide a signal representing'the third term'on the right hand side of Equation 2. Network 44 combines the various signals supplied to it in appropriate proportions and senses so as' to provide at its output-a signal representing (DDD as given by' Equation 2.

Whilst a particular system has been described in which the control laws represented by'Equations 1 and 2 are employed, it will be appreciated that these may be varied i as required forV different aircraft. Other terms Ywhich may appear in'Equation l, requiring the gener-lation of appropriate components of the demandsignalrin'addition to or'instead of some or all ofthose described, are terms dependent on: Y

(1) Any departure of the aircrafts bank attitude from level- (2) The aircrafts rudder angle 5 (las opposed to Dg in Equation l) (3)' The change of heading fDz//dt (4) The lateral pendulum position opV (as opposed to D p) and (5) VThe aircrafts rate of yaw.

' Similarly Equation 2 may include a term in and terms representing functions of r and (glo-(br) other than those described. Again, in both channels, the characteristics ofthe shaping and summing networks can be varied as required to alter the precise functions of the quantities employed andthe proportions in which they are combined.

The lateral accelerometer employed in theV system described is a lateral pendulum but other types of accelerometer may be employed.

Throughout the description, no mention' has been made of the nature of the signals employed and it will be appreciated that those may be A C. or DC. signals as convenient and that a mixture of the two may be employed provided that modulators and demodulators are included in known manner so that, where signals are combined, they are of the same kind. Further whilst the system described employs as a basic automatic pilot one utilising the rate/rate system of control, a position control automatic pilot can equally well be employed with corresponding modification of the control laws.

While there have been described above what are presently believed to be the preferred forms of the invention, variations thereof will be obvious to those skilled in the art and all such changes and Variations which fall within* the spirit ofthe invention are intended to be The outputs of the two yparallel channels in network 45 are combined in suitable proportions, the y a landing maneuver of an aircraft, comprising means responsive to lateral acceleration of the aircraft to provide a signal dependent upon said lateral acceleration, means responsive to said signal to provide a demand for maneuver of the aircraft in bank which demand is dependent upon said lateral acceleration in a sense to oppose tendency for roll of the aircraft arising with said lateral acceleration, and means responsive to said bankdemand for controlling the aircraft in bank in accordance withA the demand.

2. An automatic flight control system according to claim 1 wherein said means responsive to the bankdemand comprises means to control ailerons ofthe aircraft in accordance with the demanded maneuver in bank.

3. An automatic flight control system according to vclaim 1, means responsive to maneuver of the aircraft inl bank* to provide a signal dependent upon the bank maneuver, said means for providing the bank-demandV beingresponsive to the bank-maneuver signal to include in the bank-demand a component dependent upon such signal.

4. An automatic flight control-system according to claim 3 wherein said means to provide the bank-maneu-v ver signal produces aV signal dependent upon rate of change of bank.

5. An automatic flight control system according to claim 4, means responsive to rateof rotation, p, of the aircraft about its fore-aft axis to provide a measure of the rate p, means responsive to rate of yaw, r, of the aircraft to provide a measure of the rate r, means responsive to pitch angle 0 of the aircraft to provide a measure of angleY 0, and means to provide in accordance with said measures of p, r, and 0 a signal dependent upon the function (p-l-r) to constitute said signal dependent upon rate of change of bank. g

6. An automatic night control system according to claim 4, a phase-advancing network, and means for supplying said bank-maneuver signal via the phase-advancing network to said means for providing the bank-demand.

7. An automatic Hight control system according to claim 1, means responsive to yaw of the aircraft to provide a signal dependent upon a function of yaw, said means for providing the bank-demand being responsive to the last-mentioned signal to include in the bank-demand a component which is dependent upon said function of yaw and `which is in a sense to oppose tendency Vof theaircraft to roll in response to yawing movement claim l, means responsive to angular movement of the aircrafts rudder to provide a signal dependent upon a function ofthe rudder-position, said means for providing the bank-demand being responsive to the last-mentioned signal to include in thebank-demand a component dependent upon said function of rudder-position.

9. An automatic flight control system according to claim l wherein saidrmeans responsive to lateral acceleration has a pendulum mounted for angular deflection about an axis parallel Yto the fore-aft axis of the aircraft, and said signal dependent upon the lateral acceleration is dependent upon angular deflection of the pendulum.

10. An automatic flight control system according to claim 9 wherein said pendulum is mounted forward of the center of gravity ofthe aircraft.

11. An automatic flight control system for use during a landing maneuver of anaircraft, comprising means responsive to lateral acceleration of the aircraft to provide a signal dependent upon said lateral acceleration, means responsive to said signal to provide a `demand for movement of ailerons of the aircraft which demand has va comportent that is dependent upon said lateral acceleration and is in a sense to oppose tendency of the aircraft to roll, and a servo channel responsive to said demand to control the ailerons in accordance with the demand.

12. An automatic iiight control system according to claim 11, means for providing a signal dependent upon a function of angular position of the ailerons, means for providing a signal dependent upon diiference between actual and desired headings of the aircraft, and means responsive to the last-mentioned two signals for controlling the rudder of the aircraft in accordance with the function of angular position of the ailerons and the heading difference.

13. An automatic night control system according to claim 12, means responsive to yaw of the aircraft to provide a signal dependent upon a function of the rate of yaw, the means for controlling the rudder being responsive to such signal to control the rudder in accordance with said function of yaW-rate.

14. An automatic ight control system for use during a landing maneuver of an aircraft, comprising a lateral pendulum to provide a signal dependent upon pendulum displacement-angle resulting from lateral acceleration ofthe aircraft, means responsive to said signal to provide a demand for movement of ailerons ofthe aircraft which demand has a component that is dependent upon the displacement-angle and is in a sense to oppose tendency of the aircraft to roll, and a servo channel responsive to said demand to control the ailerons in accordance with the demand.

15. An automatic ght control system for use during a landing maneuver of an aircraft, comprising means responsive to lateral acceleration of the aircraft to provide a first signal dependent upon said lateral acceleration, means for providing a second signal dependent upon movement of the aircraft rudder, means responsive to said rst and second signals to derive a signal which is representative of a demand for movement of ailerons of the aircraft and which has two components that are dependent respectively upon said lateral acceleration and rudder movement in a sense to oppose tendency of the aircraft to roll, and a servo channel for controlling the ailerons in accordance with said demand.

16. An automatic flight control system for use during a landing maneuver of an aircraft, comprising means responsive to lateral acceleration of the aircraft to provide a first signal dependent upon said lateral acceleration, means for providing a second signal dependent upon movement of the aircraft rudder, means for providing a third signal dependent upon movement of the aircraft ailerons, means for providing a fourth signal dependent upon difference between actual and desired headings of the aircraft, means for controlling the ailerons of the aircraft in accordance with said first and second signals so as to oppose tendency of the aircraft to roll, and means for controlling the rudder of the aircraft in accordance with said third and fourth signals. 

1. AN AUTOMATIC FLIGHT CONTROL SYSTEM FOR USE DURING A LANDING MANEUVER OF AN AIRCRAFT, COMPRISING MEANS RESPONSIVE TO LATERAL ACCELERATION OF THE AIRCRAFT TO PROVIDE A SIGNAL DEPENDENT UPON SAID LATERAL ACCELERATION, MEANS RESPONSIVE TO SAID SIGNAL TO PROVIDE A DEMAND FOR MANEUVER OF THE AIRCRAFT IN BANK WHICH DEMAND IS DEPENDENT UPON SAID LATERAL ACCELERATION IN A SENSE TO OPPOSE TENDENCY FOR ROLL OF THE AIRCRAFT ARISING WITH SAID LATERAL ACCELERATION, AND MEANS RESPONSIVE TO SAID BANKDEMAND FOR CONTROLLING THE AIRCRAFT IN BANK IN ACCORDANCE WITH THE DEMAND. 